1. Field of the Invention
The present invention relates to a laser apparatus in which one or more optical components (including, for example, a condensing lens) and one or more holders for the one or more optical components are directly or indirectly fixed to a main body by adhesion. The present invention also relates to a method for assembling the above laser apparatus.
2. Description of the Related Art
Some known types of laser apparatuses optically combine a plurality of laser beams in a single optical fiber, and output a high-power laser beam by inputting the plurality of laser beams into the single optical fiber. For example, such laser apparatuses are disclosed in U.S. Pat. No. 6,995,912 and Japanese Unexamined Patent Publication No. 2004-134641. The disclosed laser apparatuses are basically constituted by one or more semiconductor lasers which emit a plurality of laser beams, a single optical fiber, and an optical condensing system which condenses the plurality of laser beams, and couples the condensed laser beams to the optical fiber.
In the above laser apparatuses, the dimensions of the optical components including collimator lenses and a condensing lens (which constitute an optical condensing system) and the holders (which hold the optical components) are normally very small. Conventionally, in order to fix the above small parts to the main body of the laser apparatus, fixing structures using an adhesive are widely used, for example, as indicated in Japanese Unexamined Patent Publication No. 2004-134641.
However, in the conventional structures in which small optical components and holders are fixed to a main body of an apparatus as mentioned above, the positions in which the optical components and holders are fixed are likely to be inclined from desired positions.
The above problem is explained in detail below by taking as examples laser apparatuses in which semiconductor lasers, an optical condensing system, and a near-end portion of an optical fiber on the light-entrance side are arranged in a package.
In the first example of the laser apparatus, the near-end portion of the optical fiber is fixed in such a manner that the core axis of the near-end portion is parallel to the bottom surface of the package, a holder having a rectangular parallelepipedic shape and being arranged to fix a lens is fixed on the bottom surface of the package, and a condensing lens is adhesively fixed on the upper surface of the holder in such a manner that the core axis of the near-end portion of the optical fiber coincides with the optical axis of the condensing lens. The condensing lens is a truncated lens having a shape obtained by cutting out a portion of an axisymmetric round lens with planes parallel to the optical axis of the condensing lens, and a surface of the condensing lens exposed by cutting with a plane becomes an adhesion surface. Thus, the condensing lens is fixed to the upper surface of the holder in such a manner that the adhesion surface of the condensing lens is in contact with the upper surface of the holder.
In order to make the optical axis of the condensing lens coincide with the core axis of the near-end portion of the optical fiber when the above condensing lens is adhesively fixed, it is necessary that the optical axis of the condensing lens be parallel to the bottom surface of the package. It may be considered that the optical axis of the condensing lens will be set parallel to the bottom surface of the package by simply pressing the condensing lens against the upper surface of the holder (i.e., by letting the adhesion surface of the condensing lens fit the upper surface of the holder) when the upper surface of the holder is parallel to the bottom surface of the package.
However, according to research carried out by the present inventors, it has been found that sometimes the optical axis of the condensing lens may not become parallel to the bottom surface of the package even when the adhesion surface of the condensing lens fits the upper surface of the holder. This is because the orientation of the condensing lens can vary according to the direction and distribution of the pressing force and the like when the condensing lens is pressed against the upper surface of the holder. Although the inclination of the condensing lens fixed in the above manner is slight, the slight inclination of the condensing lens causes misalignment between the optical axis of the condensing lens and the core axis of the near-end portion of the optical fiber, so that the input efficiency of the laser beams which is condensed by the condensing lens and enters the optical fiber is reduced.
In the above first example in which the problem occurs, a holder is fixed on the bottom surface of the package, and the condensing lens (as an optical component) is adhesively fixed to the holder. On the other hand, in the second example of the laser apparatus, a holder to which an optical component is to be fixed is fixed as a submount to a mount which is fixed to a bottom surface of a package. In the second example, the holder can also be adhesively fixed with an inclination from the fixed mount for a reason similar to the first example. For example, in the case where the holder as the submount has a rectangular parallelepipedic shape, and a side surface of the holder is adhesively fixed to a vertical surface of the fixed mount, and an optical component such as a lens is fixed on the upper surface of the holder, it may be considered that the upper surface of the holder becomes level when the side surface of the holder is adhesively fixed to the vertical surface of the fixed mount in such a manner that the side surface (as an adhesion surface) of the holder fits the vertical surface (as a mounting surface) of the fixed mount. However, the side surface of the holder can be fixed to the mounting surface of the fixed mount with an inclination from the mounting surface of the fixed mount for a similar reason to the aforementioned first example.
In the above examples, the problems arise in the laser apparatuses in which a plurality of laser beams enter a single optical fiber and are optically combined. However, even in other laser apparatuses, similar problems can also occur, i.e., an adhesion surface of an optical component such as a lens or a holder for fixing an optical component can be fixed to a mounting surface of a member arranged on the main body side of each laser apparatus with an inclination from the mounting surface.